Characterization of a staphylococcal plasmid related to pUB110 and carrying two novel genes, vatC and vgbB, encoding resistance to streptogramins A and B and similar antibiotics

Abstract

We isolated and sequenced a plasmid, named pIP1714 (4,978 bp), which specifies resistance to streptogramins A and B and the mixture of these compounds. pIP1714 was isolated from a Staphylococcus cohnii subsp. cohnii strain found in the environment of a hospital where pristinamycin was extensively used. Resistance to both compounds and related antibiotics is encoded by two novel, probably cotranscribed genes, (i) vatC, encoding a 212-amino-acid (aa) acetyltransferase that inactivates streptogramin A and that exhibits 58.2 to 69.8% aa identity with the Vat, VatB, and SatA proteins, and (ii) vgbB, encoding a 295-aa lactonase that inactivates streptogramin B and that shows 67% aa identity with the Vgb lactonase. pIP1714 includes a 2,985-bp fragment also found in two rolling-circle replication and mobilizable plasmids, pUB110 and pBC16, from gram-positive bacteria. In all three plasmids, the common fragment was delimited by two direct repeats of four nucleotides (GGGC) and included (i) putative genes closely related to repB, which encodes a replication protein, and to pre(mob), which encodes a protein required for conjugative mobilization and site-specific recombination, and (ii) sequences very similar to the double- and single-strand origins (dso, ssoU) and the recombination site, RSA. The antibiotic resistance genes repB and pre(mob) carried by each of these plasmids were found in the same transcriptional orientation.

FIG. 1

Physical map of the S. cohnii subsp. cohnii plasmid pIP1714 (4,978 bp).

FIG. 2

Alignment of the nucleotide sequences flanking the sso_U sequences (previously named palU) and the repB gene of five plasmids: pUB110 (24), pIP1714 (this study), pIP823 (7), pTB913 (27), and pBC16 (29), also named pNS1981 (31). Dashes represent the nt which are identical to those of pUB110 (24). The direct GGGC repeats (DR) delimiting the conserved part of the plasmids are boxed, and the inverted repeats overlapping the direct repeats are indicated by arrows.